control device for an electrical vacuum pump and method for activating an electrical vacuum pump

ABSTRACT

A control device for an electrical vacuum pump includes: a determination unit designed for the purpose of detecting an operating parameter of the electrical vacuum pump, which is dependent on an operating duration of the electrical vacuum pump, and detecting a controlled variable for the electrical vacuum pump, a switching unit designed for the purpose of activating or deactivating the electrical vacuum pump as a function of a comparison of the controlled variable to at least one setpoint value, and a regulating unit designed for the purpose of changing the at least one setpoint value of the controlled variable as a function of the operating parameter.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a control device for an electricalvacuum pump and a method for activating an electrical vacuum pump, inparticular in motor vehicles having a brake booster.

2. DESCRIPTION OF THE RELATED ART

Electrical vacuum pumps are used in motor vehicles to generate a partialvacuum in the vacuum chamber of a brake booster. The electrical vacuumpump may be used as the sole vacuum source or in addition to a furthervacuum source, for example, an internal combustion engine or amechanical vacuum pump.

The electrical vacuum pump is conventionally activated using the partialvacuum, which is measured in the vacuum chamber of the brake booster, orthe pressure difference in the brake booster as a controlled variable.When the differential pressure falls below a predefined lower thresholdvalue, i.e., when the partial vacuum in the vacuum chamber of the brakebooster becomes excessively low, the electrical vacuum pump isactivated, to build up a higher differential pressure again. If apredefined upper threshold value is exceeded, i.e., if the partialvacuum in the vacuum chamber of the brake booster has again assumed adimension sufficient for the proper operation of the brake booster, theelectrical vacuum pump is deactivated again.

Electrical vacuum pumps are designed differently with respect to theirthermal carrying capacity. During the operation of the electrical vacuumpumps, their operating temperature increases with the running time. Ifthe operating temperature of an electrical vacuum pump exceeds apredetermined critical temperature, thermal overload and thereforedefects of the electrical vacuum pump may occur. Therefore, electricalvacuum pumps usually may not be in operation continuously and mustadhere to a predetermined ratio of operating time to non-operating time.

U.S. patent application publication US 2006/0158028 A1 describes amethod for activating an electrical vacuum pump of a brake booster. Toprotect the electrical vacuum pump, a minimum velocity of the vehicle isdetermined, below which activation of the electrical vacuum pump isprevented.

BRIEF SUMMARY OF THE INVENTION

The present invention is based on the idea of designing the activationof an electrical vacuum pump in such a way that the critical temperatureof the electrical vacuum pump is reached only seldom or not at all, sothat automatic deactivation of the electrical vacuum pump does not occurin critical driving situations. The higher the cumulative operatingduration of the electrical vacuum pump in a preceding predetermined timespan, the lower is the upper setpoint value of the controlled variableset, to avoid a high load of the electrical vacuum pump in a shortperiod of time. The activation of the electrical vacuum pump thereforeis carried out adaptively and may dynamically regulate the temporarycumulative operating duration of the electrical vacuum pump in anoncritical range.

The present invention therefore provides, according to one specificembodiment, a control device for an electrical vacuum pump, having adetermination unit, which is designed for the purpose of detecting anoperating parameter of the electrical vacuum pump, which is dependent onan operating duration or a temperature of the electrical vacuum pump,and detecting a controlled variable for the electrical vacuum pump, aswitching unit, which is designed for the purpose of activating ordeactivating the electrical vacuum pump as a function of a comparison ofthe controlled variable to at least one setpoint value, and a regulatingunit, which is designed for the purpose of changing the at least onesetpoint value of the controlled variable as a function of the operatingparameter.

Furthermore, according to one specific embodiment, the present inventionprovides a system having an electrical vacuum pump, which is designedfor the purpose of generating a partial vacuum for a brake booster in amotor vehicle, and a control device according to the present invention,which is designed for the purpose of activating the electrical vacuumpump.

In addition, according to one specific embodiment, the present inventionprovides a method for activating an electrical vacuum pump, having thesteps of detecting an operating parameter of the electrical vacuum pump,which is dependent on an operating duration or a temperature of theelectrical vacuum pump, detecting a controlled variable for theelectrical vacuum pump, changing at least one setpoint value of thecontrolled variable as a function of the operating parameter, comparingthe controlled variable to the at least one setpoint value to generate acontrol signal, and changing the operating state of the electricalvacuum pump as a function of the control signal.

In one advantageous specific embodiment, the control device may includea runtime counter, which is designed for the purpose of ascertaining theoperating parameter, which is dependent on the percentage totaloperating duration of the electrical vacuum pump, and providing theoperating parameter to the determination unit. The relative operatingduration of the electrical vacuum pump may thus be determined.

The runtime counter may preferably be designed for the purpose ofincrementing the operating parameter at uniform time intervals while theswitching unit keeps the electrical vacuum pump in the activated state,and decrementing the operating parameter at uniform time intervals whilethe switching unit keeps the electrical vacuum pump in the deactivatedstate. The operating duration of the electrical vacuum pump may thus beobtained in a simple way as a cumulative value.

The controlled variable may advantageously be a partial vacuum generatedby the electrical vacuum pump, the at least one setpoint value includingan upper threshold value, and the switching unit being designed for thepurpose of deactivating the electrical vacuum pump if the partial vacuumexceeds the upper threshold value. In this way, a temporary earlyshutdown of the electrical vacuum pump may occur if an overload of theelectrical vacuum pump is imminent. This reduces in particular theprobability that the electrical vacuum pump must be automaticallydeactivated in real driving operation of a motor vehicle.

In one preferred specific embodiment of the method according to thepresent invention, the at least one setpoint value may be reduced by apredetermined amount if the operating parameter exceeds a parameterthreshold value. A simple setpoint value adaptation may thus take placein one or multiple discrete setpoint value steps.

In one alternative specific embodiment, the at least one setpoint valuemay be continuously lowered with an increase of the operating parameter.A uniform reduction of the deactivation threshold and a finelyadjustable threshold value adaptation are thus carried out.

In one advantageous specific embodiment of the method according to thepresent invention, the detection of the operating parameter may includedetecting the operating temperature of the electrical vacuum pump. Thishas the advantage that a temperature model may be used, which specifiesthe dependence of the operating temperature of the electrical vacuumpump on the operating duration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a system having an electrical vacuumpump in a motor vehicle according to one specific embodiment of thepresent invention.

FIG. 2 shows a schematic view of a method for activating an electricalvacuum pump according to another specific embodiment of the presentinvention.

FIG. 3 a shows a schematic view of a characteristic curve graph for theactivation of an electrical vacuum pump according to another specificembodiment of the present invention.

FIG. 3 b shows a schematic view of a characteristic curve graph for theactivation of an electrical vacuum pump according to another specificembodiment of the present invention.

FIG. 4 shows graphs of the time curve of a differential pressure and anoperating duration of an electrical vacuum pump during an activation ofthe electrical vacuum pump according to another specific embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the figures of the drawings, identical and functionally identicalelements, features, and components—if not otherwise noted—are eachprovided with the same reference numerals. It is understood thatcomponents and elements in the drawings are not necessarily shown toscale to one another for the sake of clarity and comprehensibility.

FIG. 1 shows a schematic view of a system 10 having an electrical vacuumpump 13 in a motor vehicle. System 10 includes a control device 12, anelectrical vacuum pump 13, which is activated by control device 12, abrake booster 14, and optionally a further vacuum source 15. Furthervacuum source 15 may be, for example, an internal combustion engine ofthe motor vehicle or a mechanical vacuum pump. Electrical vacuum pump 13and optionally further vacuum source 15 are designed for the purpose ofgenerating a partial vacuum in a vacuum chamber of brake booster 14.

Control device 12 and electrical vacuum pump 13 may be included in anoverall system unit 11. It may also be possible that control unit 12 isintegrated into the electronics of electrical vacuum pump 13.Alternatively, control device 12 may be implemented in an engine controlunit or another control unit of a motor vehicle. Control device 12includes a determination unit 12 a, a switching unit 12 d, and aregulating unit 12 c. Furthermore, control device 12 may include aruntime counter 12 b.

Switching unit 12 d is designed for the purpose of activating ordeactivating electrical vacuum pump 13 as a function of a comparison ofa controlled variable to one or multiple setpoint values. For example,switching unit 12 d may activate electrical vacuum pump 13 if a partialvacuum or a pressure difference in the vacuum chamber of brake booster14 sinks below a lower threshold value. In this case, electrical vacuumpump 13 is put into an active operating state to increase the partialvacuum of brake booster 14. When the partial vacuum or the pressuredifference generated by electrical vacuum pump 13 is sufficiently large,i.e., when the partial vacuum exceeds an upper threshold value,switching unit 12 d may again deactivate electrical vacuum pump 13. Thesetpoint values may include the lower threshold value and the upperthreshold value.

Determination unit 12 a is designed for the purpose of detecting thecontrolled variable of electrical vacuum pump 13, for example, a partialvacuum or a pressure difference in the vacuum chamber of brake booster14.

Furthermore, determination unit 12 a is designed for the purpose ofdetecting an operating parameter of electrical vacuum pump 13, which isdependent on an operating duration or a temperature of electrical vacuumpump 13. The operating parameter may be a count of runtime counter 12 b,for example. The count of runtime counter 12 b may be incremented atuniform time intervals for this purpose, while switching unit 12 d keepselectrical vacuum pump 13 in the activated state.

Similarly, the count of runtime counter 12 b may be decremented atuniform time intervals while switching unit 12 d keeps electrical vacuumpump 13 in the deactivated state. In this way, the operating parametermay represent a measure of the cumulative operating duration ofelectrical vacuum pump 13. In particular, the operating parameter mayspecify a percentage value, during which electrical vacuum pump 13 wasin an active operating state over a predetermined time span in the past.In other words, the operating parameter may provide information abouthow high the load of electrical vacuum pump 13 is. The higher theoperating parameter, the longer the cumulative operating time ofelectrical vacuum pump 13.

Alternatively, it is also possible that the operating parameter is avalue which specifies the operating temperature of electrical vacuumpump 13. For example, the operating parameter may be estimated via atemperature model of electrical vacuum pump 13. In particular in casesin which, for example, after the entire system is activated, runtimecounter 12 b still has a very low value, but the operating temperaturealready has a high initial value because of external influences, it maybe advantageous to use the operating temperature as the operatingparameter instead of the runtime counter content.

Regulating unit 12 c is designed for the purpose of changing thesetpoint value(s) of the controlled variable as a function of theoperating parameter. For example, regulating unit 12 c may raise orlower the upper threshold value for the partial vacuum, depending on howhigh the cumulative operating duration of electrical vacuum pump 13 ispresently at the instantaneous point in time. Regulating unit 12 c maysimilarly also raise or lower the lower threshold value for the partialvacuum depending on how high the cumulative operating duration ofelectrical vacuum pump 13 is presently at the instantaneous point intime.

FIG. 2 shows a schematic view of a method 20 for activating anelectrical vacuum pump, in particular electrical vacuum pump 13 inFIG. 1. Method 20 may be carried out, for example, by control device 12in FIG. 1.

In a first step 21, an operating parameter of the electrical vacuum pumpis detected, which is dependent on an operating duration of theelectrical vacuum pump, and a controlled variable for the electricalvacuum pump is detected. In a second step 22, at least one setpointvalue of the controlled variable is changed as a function of theoperating parameter.

In a third step 23, the controlled variable is compared to the at leastone setpoint value to generate a control signal. In a fourth step 24,the operating state of the electrical vacuum pump is changed as afunction of the control signal.

With reference to FIGS. 3 a, 3 b, and 4, an exemplary specificembodiment of the method in FIG. 2 is described in greater detailhereafter. In the exemplary specific embodiment, the at least onesetpoint value is changed by raising or lowering an upper thresholdvalue pT for the partial vacuum. However, it is understood that a changeof the at least one setpoint value may also include raising or loweringa lower threshold value for the partial vacuum.

FIG. 4 shows graphs of the time curve of a differential pressure and anoperating duration of an electrical vacuum pump during an activation ofthe electrical vacuum pump. In first graph 40, the time curve of thepartial vacuum generated by electrical vacuum pump 13 or of differentialpressure p is shown as the detected controlled variable in brake booster14. In second graph 41, which represents the same time curve as graph 40in the abscissa, the activation signal of switching unit 12 d forelectrical vacuum pump 13 is shown. An activation signal of logical zerokeeps electrical vacuum pump 13 in an inactive operating state, i.e., ina deactivated operating state, while an activation signal of logical onekeeps electrical vacuum pump 13 in an active operating state, i.e., inan activated operating state. In third graph 42, which represents thesame time curve as graph 40 in the abscissa, the time curve of operatingparameter x, in particular the count of runtime counter 12 b, is shown.The actual value of the operating parameter may be an arbitrarilyestablished numerical value, which is only defined for comparisonpurposes. In particular, the operating parameter may assume discretevalues at incremental intervals, for example, integral or naturalnumbers. The discrete values are not shown in FIG. 4 for the sake ofclarity and comprehensibility.

FIG. 4 shows an exemplary simulation in which electrical vacuum pump 13is repeatedly activated and deactivated again. At the beginning,electrical vacuum pump 13 is activated by switching unit 12 d. Partialvacuum p increases because of the evacuation activity of electricalvacuum pump 13, while electrical vacuum pump 13 is in an activeoperating state. When partial vacuum p has reached a threshold value pT,switching unit 12 d may set the activation signal in graph 41 to logicalzero, to deactivate electrical vacuum pump 13. Because of the evacuationactivity of electrical vacuum pump 13, which is no longer existent,partial vacuum p no longer increases. For example, partial vacuum p mayremain constant at the level of upper threshold value pT. It may also bepossible that partial vacuum p decreases again.

While electrical vacuum pump 13 was activated, operating parameter xrose from the (exemplary) value zero to a value greater than zero. Forexample, operating parameter x may be incremented by a runtime counterat periodic time intervals by a predetermined amount, as long as theactivation signal in graph 41 assumes the value of logical one. This mayresult in an increase of the value of operating parameter x with aconstant slope. As soon as switching unit 12 d again deactivateselectrical vacuum pump 13, the operating parameter may be decrementedagain by the predetermined amount at the periodic time intervals. Thismay result in a drop of the value of operating parameter x having aconstant gradient. In this way, operating parameter x reflects thecumulative percentage operating duration of electrical vacuum pump 13.

If partial vacuum p—as shown in the simulation in graph 40—falls below alower threshold value, switching unit 12 d may be designed for thepurpose of putting electrical vacuum pump 13 back into an activeoperating state. The value of operating parameter x may be incrementedagain in this case. The lower threshold value has been shown to beconstant over the operating duration of electrical vacuum pump 13 in thepresent exemplary embodiment. However, it is also possible to design thelower threshold value to be dynamically variable, i.e., to change thelower threshold value as a function of the parameter threshold valuesexplained hereafter.

While electrical vacuum pump 13 is now in an activated state, it mayoccur that the value of operating parameter x increases above a firstparameter threshold value x1, as indicated in graph 42 at point in timet1. Regulating unit 12 c may be designed in this case for the purpose ofchanging, for example, reducing, upper threshold value pT. Regulatingunit 12 c may resort to a characteristic curve for this purpose, whichspecifies the relationship between the value of operating parameter xand the change of upper threshold value pT.

Exemplary characteristic curves are shown in the graphs of FIGS. 3 a and3 b. In FIG. 3 a, characteristic curve 30 a is a step function. If thevalue of operating parameter x is above first parameter threshold valuex1, regulating unit 12 c is designed for the purpose of adapting upperthreshold value pT by change amount Δ=0, i.e., upper threshold value pTremains at the predefined value. However, if the value of operatingparameter x is above first parameter threshold value x1, but below asecond parameter threshold value x2, regulating unit 12 c is designedfor the purpose of adapting upper threshold value pT by change amountΔ=Δ1. Finally, if the value of operating parameter x is above secondparameter threshold value x2, regulating unit 12 c is designed for thepurpose of adapting upper threshold value pT by change amount Δ=Δ2.

In the exemplary time curve of FIG. 4, regulating unit 12 c may bedesigned, for example, for the purpose of lowering upper threshold valuepT by amount Δ1 from point in time t1. This is indicated in graph 40 bylowered threshold value pT-Δ1. If partial vacuum p increases due to theevacuation activity of electrical vacuum pump 13, switching unit 12 d isdesigned for the purpose from point in time t1 of comparing controlledvariable p to the changed upper threshold value, i.e., to the reducedupper threshold value. If partial vacuum p thus reaches upper thresholdvalue pT-Δ1, switching unit 12 d is designed for the purpose of againdeactivating electrical vacuum pump 13.

After the controlled variable falls below the lower threshold valueagain, switching unit 12 d again activates the electrical vacuum pump.Similarly as explained with reference to point in time t1, operatingparameter x increases above second parameter threshold value x2 at pointin time t2, so that regulating unit 12 c decreases upper threshold valuepT-Δ1 again to pT-Δ2.

In this way, a dynamic adaptation of upper threshold value pT to theoperating duration of electrical vacuum pump 13 is carried out, so thatin the event of higher load of electrical vacuum pump 13, the run timesare shortened. Accordingly, regulating unit 12 c may raise upperthreshold value pT again in the event of a lower load of electricalvacuum pump 13, as shown in FIG. 4 as an example at point in time t4, ifoperating parameter x sinks below the parameter threshold values.

FIG. 3 b shows an alternative characteristic curve 30 b for regulatingunit 12 c. Characteristic curve 30 b is composed of interpolated partialsections between parameter threshold values x3, x4, x5, and x6, so thatin the event of a change of operating parameter x, a continuousadaptation of upper threshold value pT results. It is clear that thecharacteristic curves shown in FIGS. 3 a and 3 b are only of anexemplary nature, and the number of the parameter threshold values, thegradients of the characteristic curves, and the values of change amountsmay assume other arbitrary values.

Corresponding characteristic curves as shown in FIG. 3 a or 3 b may alsobe specified for the lower threshold value. The characteristic curvesfor the lower threshold value may be set equal to the characteristiccurves for the upper threshold value, for example.

1-10. (canceled)
 11. A control device for an electrical vacuum pump,comprising: a determination unit configured to (i) detect an operatingparameter of the electrical vacuum pump, wherein said operatingparameter is dependent on one of an operating duration or a temperatureof the electrical vacuum pump, and (ii) detect a controlled variable forthe electrical vacuum pump; a switching unit configured to one ofactivate or deactivate the electrical vacuum pump as a function of acomparison of the controlled variable to at least one setpoint value;and a regulating unit configured to change the at least one setpointvalue as a function of the operating parameter.
 12. The control deviceas recited in claim 11, further comprising: a runtime counter configuredto (i) ascertain the operating parameter, wherein said operatingparameter is dependent on a percentage total operating duration of theelectrical vacuum pump, and (ii) provide the operating parameter to thedetermination unit.
 13. The control device as recited in claim 12,wherein the runtime counter is configured to (i) increment the operatingparameter at uniform time intervals while the switching unit maintainsthe electrical vacuum pump in the activated state, and (ii) decrementthe operating parameter at uniform time intervals while the switchingunit maintains the electrical vacuum pump in the deactivated state. 14.The control device as recited in claim 11, wherein the controlledvariable is a partial vacuum generated by the electrical vacuum pump,the at least one setpoint value includes an upper threshold value, andthe switching unit is configured to turn off the electrical vacuum pumpwhen the partial vacuum exceeds the upper threshold value.
 15. A system,comprising: an electrical vacuum pump configured to generate a partialvacuum for a brake booster in a motor vehicle; and a control deviceconfigured to activate the electrical vacuum pump, wherein the controldevice includes: a determination unit configured to (i) detect anoperating parameter of the electrical vacuum pump, wherein saidoperating parameter is dependent on one of an operating duration or atemperature of the electrical vacuum pump, and (ii) detect a controlledvariable for the electrical vacuum pump; a switching unit configured toone of activate or deactivate the electrical vacuum pump as a functionof a comparison of the controlled variable to at least one setpointvalue; and a regulating unit configured to change the at least onesetpoint value as a function of the operating parameter.
 16. A methodfor activating an electrical vacuum pump, comprising: detecting anoperating parameter of the electrical vacuum pump, wherein saidoperating parameter is dependent on one of an operating duration or atemperature of the electrical vacuum pump; detecting a controlledvariable for the electrical vacuum pump; changing at least one setpointvalue for the controlled variable as a function of the detectedoperating parameter; comparing the detected controlled variable to theat least one setpoint value to generate a control signal; and changingthe operating state of the electrical vacuum pump as a function of thecontrol signal.
 17. The method as recited in claim 16, wherein the atleast one setpoint value is reduced by a predetermined amount if theoperating parameter exceeds a parameter threshold value.
 18. The methodas recited in claim 16, wherein the at least one setpoint value iscontinuously lowered with an increase of the operating parameter. 19.The method as recited in claim 16, wherein the controlled variable is apartial vacuum generated by the electrical vacuum pump, the at least onesetpoint value includes an upper threshold value, and the change of theoperating state includes a shutdown of the electrical vacuum pump whenthe partial vacuum exceeds the upper threshold value.
 20. The method asrecited in claim 17, wherein the operating parameter is an operatingtemperature of the electrical vacuum pump.